The molecular biology of human fetal hemoglobin (HbF) synthesis will be investigated in an attempt to define more clearly the factors which are responsible, at the subcellular level, for the regulation and control of: 1) normal HbF synthesis in human fetal red cells; 2) the neonatal switch from fetal to adult hemoglobin synthesis and 3) the persistence of HbF synthesis into adult life in various pathologic states. It is hoped that the information obtained in these studies will provide insight into possible means of increasing HbF synthesis in individuals affected by hemoglobinopathies, the clinical severity of which could be attenuated by the presence of increased levels of HbF. We plan to investigate the following aspects of the problem: 1) measure the levels of fetal (gamma chain) and adult (beta chain) messenger RNA (mRNA) by molecular hybridization assays in fetal erythroid cells at different stages of gestation and correlate these measurements to the level of gamma and beta chain synthesis in the intact red cells of the same individuals; 2) study the nucleotide sequence of gamma chain mRNA and compare it to that of beta mRNA for differences which might relate to the differential control of gamma and beta chains synthesis; 3) study the structure of gamma chain genes themselves by restriction endonuclease mapping of natural cellular DNA to define the nature of DNA sequences adjacent to the structural genes which might be involved in differential gene expression; 4) study the control of HbF synthesis in adult and fetal erythroid precursor cells in the plasma clot culture system which allows the replication and differentiation of erythroid stem cells in vitro.